Process of electrodepositing indium



Patented Mar. 15, 1932 PATENT OFFICE DANIEL GRAY, OF ONEHJA, NEW YORK, ASSIGNOR 1'0 ONEIDA OF ONEIDA, NEW YORK, A CORPORATION OF COMMUNITY, LIMITED, NEW YORK PROCESS OF ELECTRODEPOSITIN G HQ'DIUI No Drawing. Application filed November 22, 1926, Serial No. 150,158. Renewed June 5, 1981.

This invention relates to a process of elec tro-depositing indium.

The object of the invention is to provide a process by which the indium may be efficient- 5 ly and economically deposited on a suitable cathode so as to firmly adhere to said cathode.

While the rocess is suitable for electrodepositing indium on any object which can serve as a cathode, it is especially advantageous for plating indium onto a silver or silver-plated article to make said article tarnish resisting Broadly considered, the process consists in first preparing a suitable water-soluble inorganic salt of indium, for example, the sulphate, the nitrate, or any of the halide salts.

The said salts may be prepared in any suitable way as has been customary in the art heretofore, for example, by dissolving the 2 metal or the hydroxide in the corresponding inorganic acid. An aqueous solution of the inorganic salt is prepared and to this solution is added a sufficient amount of alkali, for example, sodium, potassium or ammonium hydroxide, to insure the removal of any free acid in the solution. In practice, the alkali is added until a slight rmanent precipitate is formed, the mixture i ing stirred at intervals during the addition of the alkali. To the mixture is then added an organic acid which will h 'drolyze only slowly in the presence of an alkali such, for example, as formic acid, tartaric acid, or oxalic acid. When formic acid is used, the amount employed is sufficient to give about 50 cc. of formic acid (HCOOH) per liter of the final bath. Where other organic acids are employed, they must be used in proportions suflicient to give the same acidic strength as formic acid.

The final solution is used as a bath with anodes which may be either platinum or indium. The electro-deposition may be carried out with current densities running from .025 to 2 amperes per square inch of cathode surface. The voltage employed should be about .5 to .9 volts.

The process will now be described in detail in its preferred embodiment. The metal is electro-deposited from a bath containing 0 indium chloride. The final bath may contain proportion of indium, for exfrom' about 1 gram of indium per liter of the bath up to grams per liter. In practice, very advantageous results have been obtained by employing a bath containin 40 grams per liter. The bath is made by first preparing an aqueous solution of indium chloride, preferably with a minimum amount of water. When the solution is complete, ammonium hydroxide is carefully added with stirring until a slight permanent precipitate is formed. To the mixture is added an organic acid, for example, formic acid, preferably of about 85% strength, in such a quantity that when the solution is made up to final volume, there will be about cc. of formic acid per liter of the completed bath. Then the "additional water is added to bring the solution up to its final v'olum'e, when it will contain the amount of indium figured as metal determined upon for the bath.

In this bath it is advantageous to use anodes of indium, because the indium of the anode is dissolved in the bath as the indium in the bath-is plated out, thus maintaining the strength of the bath in a satisfactory manner. Of course,-if desired, an inert anode, m'ost advantageously platinum, ma be employed, and as the indium stren of the bath is reduced, it may be brought up to the desired standard from time to time by the addition of the requisite amount of indium chloride.

The article to be plated, that is to say, the cathode, for example, silver or silver-plated ware, mustbe cleaned in the usual way for preparing articlesto be plated.

With a voltagefbetween .5 and .9 volts, the current density may .be varied considerably and satisfactory results obtained. While, as hereinbefore stated, the current density may vary from .025 to '2 amperes per square inch of cathode surface, it has been found in practice that a density of .10 to .15 gives very advantageous results.

The temperature of the bath may vary considerably without seriously affecting the results, for example, from 18 C. to ;100 (3.,

any desired ample,

7 bath about from 20 formic acid but it has been found advisable to keep the C. to 28 C.

During the plating operation, particularly where the indium is being deposited upon silver or silver-plated articles, it will be found advantageous to agitate the bath, for example, by stirring it, although good results have been obtained without stlrring.

The use of formic acid, or some other organic acid which will hydrolyze only slow-' ly in the presence of an alkali, is very important. It is likely that such an acid serves to keep the hydrogen ion concentration substantially constant.

What is claimed is:

1. The process of electro-depositing indium, which comprises preparing an aqueous solution containing indium chloride, adding ammonium hydroxide to this solution until a slight precipitate is formed, then adding a water-soluble organic acid which 'will hydrolyze slowly in the presence of an alkali, and passing a direct current through electrodes immersed in the bath, whereby the indium is deposited on the cathode.

2. The process of electro-depositing indium, which consists in preparing an aqueous solution containing indium chloride, adding ammonium hydroxide to this solution until a slight precipitate is formed, then adding formic acid to the solution and passing a direct current through electrodes immersed in the bath, whereby the indium is deposited on the cathode. I

3. The process of electro-depositing indium, which consists in preparing an aqueous solution containing indium chloride, adding ammonium hydroxide tothis solution until a slight precipitate is formed, then adding formic acid to the solution and passing a direct current through electrodes immersed in the bath while maintaining the current density between .025 and 2.0 amperes per square inch of cathode surface, whereby the indium is deposited on the cathode.

4. The process of electro-depositing indium, which consists in preparing an aqueous solution containing indium chloride, adding ammonium hydroxide to this solution until a slight precipitate is formed, then adding to the solution and passing a direct current through electrodes immersed in the bath while maintaining the bath at a, temperature not less than 18 C. and not greater than 100 (1., whereby the indium is deposited on the cathode.

5. The process of electro-depositing indium, which comprises preparing an aqueous solution containing indium chloride, adding an alkali to this solution until a slight precipitate is formed, then adding a water soluble organic acid which will hydrolyze slow- 1 in the presence of an alkali, and passing a irect current through electrodes immersed in the bath, whereby the indium is deposited on the cathode.

6. The process of electro-depositing indin testimony whereof, I have hereunto set my hand.

DANIEL GRAY. 

